Stage @@toStringTag (--harmony-tostring)

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index d17f64facba134f1bc03770c5f97c7aecc8f7124..1460315dbb60189a6e0ffbb785d8d0a001e79998 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -169,13 +169,13 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_object_literals, "harmony object literal extensions") \
   V(harmony_regexps, "harmony regular expression extensions")     \
   V(harmony_arrow_functions, "harmony arrow functions")           \
-  V(harmony_tostring, "harmony toString")                         \
   V(harmony_proxies, "harmony proxies")                           \
   V(harmony_templates, "harmony template literals")               \
   V(harmony_sloppy, "harmony features in sloppy mode")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
-#define HARMONY_STAGED(V)                      \
+#define HARMONY_STAGED(V)                 \
+  V(harmony_tostring, "harmony toString") \
   V(harmony_scoping, "harmony block scoping")
 
 // Features that are shipping (turned on by default, but internal flag remains).